a) Field of the Invention
This invention relates to photosensitive compositions of the bichromate/water-soluble high-molecular substance, and more specifically to photosensitive compositions each of which has high sensitivity and is excellent in improving the productivity of a production process of a product by use of the photosensitive compositions.
b) Description of the Related Art
As bichromate-containing photosensitive compositions are soluble in water, permit easy handling and are available at relatively low price, they have been used widely to date as resist materials in the manufacture of machine plates, such as letterpress plates, deep-etch offset plates and screen printing plates, and also in the photoetching work of shadow masks for color cathode-ray tubes, lead frames and etched metal products.
These bichromate-containing photosensitive compositions, however, involve a problem that due to their low sensitivity to exposure light sources of high-energy radiation such as ultraviolet rays, they require long-time exposure, a high irradiation intensity of high-energy radiation and a high dose upon use, resulting in a problem that the productivity of printing press plates or photoetched products cannot be increased. Especially in the mass production of shadow masks by use of a bichromate-containing photosensitive composition of the casein or polyvinyl alcohol type, exposure requires substantial time and high-energy radiation of large irradiation energy.
An object of the present invention is, therefore, to provide a photosensitive composition which, while retaining resolution comparable with the conventional bichromate-containing photosensitive compositions, posses excellent sensitivity, enables shortening the time of exposure and decreasing the exposure of high-energy radiation, and permits an improvement in the productivity of a product.
With a view to solving the above-described problems and achieving the object, the present inventors have proceeded with an extensive investigation. As a result, it has been found that additional inclusion of a polyhydric alcohol and/or an ether in an aqueous solution of a particular water-soluble high-molecular substance, said aqueous solution containing a bichromate and/or a chromate, makes it possible to bring about extremely high sensitivity compared with the conventional bichromate-containing photosensitive compositions while retaining a resolution as high as the resolutions of these conventional photosensitive compositions and hence to shorten the time of exposure, to decrease the exposure of high-energy radiation and to improve the productivity of printing press plates or photoetched products.
The above-described object can be achieved by the present invention to be described hereinafter. Described specifically, the present invention provides a composition comprising:
(A) at least one sensitizer selected from the group consisting of bichromates and chromates;
(B) a water-soluble high-molecular substance;
(C) at least one sensitivity improver selected from the group consisting of polyhydric alcohols and ethers; and
(D) water.
The photosensitive composition according to the present invention, while retaining resolution comparable with those available from the conventional chromate-containing photosensitive compositions, has extremely high sensitivity and makes it possible to shorten the time of an exposure step, to decrease the exposure of high-energy radiation and to improve the productivity of printing press plates and photoetched products.